EUSTATIC SIGNALS IN THE JURASSIC AND LOWER CRETACEOUS (NEOCOMIAN) DEPOSITS OF THE WEST-SIBERIAN SEDIMENTARY BASIN

Abstract

A transgressive-regressive (T-R) curve for the Jurassic and Lower Neocomian of the West-Siberian sedimentary basin was constructed on a detailed chronostratigraphic basis. This curve is compared with the quantitative eustatic curve for the Russian and Siberian Platforms, constructed earlier by D. Sahagian et al. for the Middle Jurassic-Cretaceous from sedimentation and biostratigraphic data, and with the curve constructed by B. Haq et al. This comparison permitted recognizing eustatic signals from local T-R events. Nineteen significant T-R events are distinguished in the Jurassic-Neocomian: two - in the Early Jurassic, three - in the Middle Jurassic, four - in the Late Jurassic, and ten - in the Neocomian. Most of the T-R cycles are well correlated with the eustatic curves. The increase in the frequency of sea level fluctuations is explained by reduction of the regressive «shoulder» of cycles with time. Significant T-R events in the Jurassic and Neocomian were traced far beyond West Siberia, both in the adjacent regions and on other continents of the Northern Hemisphere. These are Kiterbyut T-event (Early Toarcian), Vymsk-Leontievsk T-R event (Bajocian), Central-Vasyugan R-event (Middle Oxfordian), Bazhenovka T-event (Late Kimmerigian-Volgian), and five T-R events in the Valanginian. A «through» sequence-stratigraphic analysis has been carried out for the Jurassic and Neocomian petroliferous series of the West-Siberian sedimentary basin. The series was divided into sequences of second and third ranks, which has allowed some contradictions between the existing stratigraphic and sedimentation models to be overcome.